Stabilization of chloroaromatics

ABSTRACT

Benzyl chloride, ( Alpha -chlorovinyl)toluene, and other such aromatic compounds containing labile side chain chlorine atoms are inhibited against chemical attack on aluminum by the presence of a small amount of a nitroalkane, preferably nitromethane. The nitroalkane inhibitor is particularly useful to prevent corrosion, polymerization, and decomposition during distillation and storage of such reactive chlorinated aromatics.

United States Patent [\91 Hall et al. 5] Nov. 11, 1975 STABILIZATION 0F CHLOROAROMATICS 2.517.894 8/[950 Larchar 260/6515 R x 751 Inventors: Richard H. Hall, Midland; Daniel H. Q i K i fiz z a 3.5497l5 12/1970 Cormany et ul. 260/6515 R rcer, Ian; eer es, Wellesley, all of Mich. P E v H d T M rzmar .rammerowar ars Asslgneei h Dow Chemical p Attorney, Agent, or Firm-David H. Thurston; Glwynn Midland, Mich. Baker [22] Filed: Mar. 5, 1973 {21] Appl. No.: 337,941 [57] ABSTRACT Benzyl chloride, (a-chlorovinyl)toluene, and other [52] Cl 22 such aromatic compounds containing labile side chain [51] Int Cl 2 C07C 25/14 chlorine atoms are inhibited against chemical attack [58] Fieid "56 7 8 57 on aluminum by the presence of a small amount of a 260/65] R 394 d nitroalkane, preferably nitromethane. The nitroalkane inhibitor is particularly useful to prevent corrosion, [56] References Cited polymerization. and decomposition during distillation UNITED STATES PATENTS and storage of such reactive chlorinated aromatics.

2.440.l00 4/1948 Klabunde 260/6525 R X 11 Claims, N0 Drawings STABILIZATION OF CHLOROAROMATICS BACKGROUND OF THE INVENTION This invention relates to the stabilization of aromatic compounds containing labile side chain chlorine. It relates particularly to the stabilization of such compounds in the presence of aluminum.

Aromatic compounds with aliphatic substituents having labile chlorine atoms are known to be highly reactive with metals such as aluminum and iron. Storage and processing of such compounds usually requires glass or glass-lined equipment or equipment made of or lined with expensive, highly inert metals such as nickel, tantalum etc. Aromatic compounds of this type include benzyl chloride, ethylbenzyl chloride, (or-chlorovinyU- toluene, vinylbenzal chloride, chloromethyl-naphthalene, l,2-dichloro-l-tolylethane, and the like. Pure vinylbenzyl chloride is known to be noncorrosive to aluminum under ordinary conditions, but the crude material as obtained from the gas phase chlorination of vinyltoluene and even technical or partially purified grades of this compound contain appreciable quantities t I of one or more of the reactive compounds previously listed so that the dangers of corrosion, polymerization. and destructive decomposition exist when these grades are in contact with metals such as aluminum and iron, particularly under conditions encountered during distillation. Depending upon the types of organic chlorides present, the polymerization can be either or both of vinyl polymerization and a polyalkylation reaction of the Friedel-Crafts type initiated by aluminum chloride resulting from the attack of reactive chlorides upon aluminum.

It is known to avoid decomposition and polymerization by distilling crude vinylbenzyl chloride and related compounds in the presence of a combination of an alkylene oxide and a nitroaromatic compound, see Hoffenberg et al. US. Pat. No. 3,274,077. Although this combination is effective in titanium equipment, the alkylene oxide will react with the hydrogen chloride often liberated under distillation conditions and the chlorohydrin thereby formed is corrosive to metal surfaces.

SUMMARY OF THE INVENTION other handling or processing. The chlorine-containing aromatics thereby inhibited against decomposition and corrosion or polymerization are represented by the formula wherein A is a benzene or naphthalene nucleus, Y is H or lower alkyl, R and X each are C] or H, at least one being C], R is H, CH or CH CI, m is one or two, and n is zero or one.

Nitro lower alkanes are those of 1-4 carbon atoms and include nitromethane, nitroethane, and the nitropropanes and nitrobutanes. A concentration of about 0. l5 percent by weight is effective and more can be used but is not necessary. Nitromethane is preferred. The nitroalkane inhibitor may be used in combination with one or more known polymerization inhibitors such as o-nitrophenol, and dinitro-o-cresol.

DETAILED DESCRIPTION The nitroalkane inhibitor is particularly useful in the storage, handling and shipping of benzyl chloride and in the distillation or other handling of crude vinylbenzyl chloride as obtained from the high temperature gas phase chlorination of vinyltoluene. Use of the inhibitor thereby permits the use of aluminum or iron containers or equipment which would otherwise be impractical. For example, when crude vinylbenzyl chloride containing significant amounts of (a-chlorovinyhtoluene and other reactive impurities is distilled in contact with aluminum equipment or distillation column packing, as the mixture is heated for longer periods and particularly as local concentrations of reactive impurities occur, the aluminum is corroded and insoluble polymer is formed at an increasingly rapid rate which soon causes plugging of the distillation column. The defined nitroalkane inhibitor is effective to prevent both the corrosion of aluminum and the polymerization.

EXAMPLE 1 A clean aluminum coupon (alloy 606l) was dipped in a container of benzyl chloride at C. Red spots soon appeared on the metal surface and a vigorous reaction with the metal started with darkening of the liquid and copious evolution of HCl. Addition of about one percent by weight of nitromethane at the red spot stage prevented further reaction. When the benzyl chloride initially contained the nitromethane, no visible reaction took place.

EXAMPLE 2 The procedure of Example I was repeated with (achlorovinyl)toluene in place of benzyl chloride. Essentially the same results were observed.

EXAMPLE 3 The crude reaction product from a high temperature gas phase chlorination of vinyltoluene consisted essentially of about 60% unreacted vinyltoluene, 30% vinylbenzyl chloride, 3% a-chlorovinyltoluene, and 6% L2- dichlorol-tolylethane. When this was distilled through an aluminum column to separate the (ct-chlorovinyhtoluene, there was considerable corrosion of the alumi num, fonnation of polymer in the column, and evolution of HCl. Addition of I% by weight nitromethane resulted in essential elimination of decomposition and polymerization reactions.

Addition of butylene oxide or p-dioxane, two inhibitors used to prevent reaction of methylchloroform with aluminum, in place of the nitromethane in the above distillation was ineffective to prevent the aluminum reaction.

EXAMPLES 4-7 A series of experiments was run in which 0.25 ml. of nitro compound was added to 5 ml. of benzyl chloride in a test tube, a small piece of aluminum was put in the liquid. and the upright test tube was immersed to a depth of two inches in an oil bath held at 125C. Column packing of 3003 Al was used in all experiments except with nitromethane where an aluminum tubing fitting of 5052 Al was used. Nitrocyclohexane and nitrobenzene were run for comparison. Results were as follows:

Nitro Compound Effect Obsened None '1 min. 50 sec. reaction started 3 min. sec. bubbles of HCl 4 min. 5 sec.. vigorous reaction nitroc \clohexane reaction started at 4 min. 5 sec. nitrohenzene reaction started at 4 min. 50 sec. nitromethane no visible reaction at 30 min. nitroethane no visible reaction at 30 min. 1-nitropropane no visible reaction at 30 min.

lnitropropane no visible reaction at 30 min.

EXAMPLE 8 The procedure of Examples 4-7 was repeated using ethylbenzyl chloride (mixed isomers) and 6061 Al turnings. With no inhibitor added, at 125C. reaction started at 14 minutes. With 1% by weight nitromethane present, no visible reaction occurred after 30 minutes.

EXAMPLE 9 As in Examples 4-8. l-chloromethyl naphthalene was heated at 125C. in the presence of 1 100 Al foil. With no inhibitor added, reaction started at 15 minutes. When 1% by weight of nitromethane was present, there was no visible reaction after minutes.

EXAMPLE 10 wherein A is a benzene or naphthalene nuc1eus, Y is H or lower alkyl. R and X are each C1 or H, at least one of R and X being Cl, R is H, CH or CH C1, m is one or two, and n is 0 or 1 containing as the essential stabilizer against attack by aluminum of at least about 0.1 percent by weight of a nitroalkane of 1-4 carbon atoms.

2. The composition of claim 1 wherein the nitroalkane is nitromethane.

3. The composition of claim 2 wherein the nitroalkane is present in a concentration of about 0.1-5 percent by weight.

4. The composition of claim 2 wherein the chlorinated aromatic compound is benzyl chloride.

5. The composition of claim 2 wherein the chlorinated aromatic compound is (a-chlorovinyl)toluene.

6. The composition of claim 2 wherein the chlorinated aromatic compound is the crude reaction product obtained from the high temperature gas phase chlorination of vinyltoluene.

7. The composition of claim 2 wherein the chlorinated aromatic compound is l-chloromethylnaphthalene.

8. The composition of claim 2 wherein the chlorinated aromatic compound is ethylbenzyl chloride.

9. The composition of claim 2 wherein the chlorinated aromatic compound is a,a-dichloro-p-xy1ene 10. The composition of claim 1 wherein the nitroalkane is nitroethane.

ii. The composition of claim 1 wherein the nitroal kane is a nitropropane.

UNITED STATES PATENT AND TRADEMARK OFFICE PATENT NO.

DATED INVENTORKS) CERTIFICATE OF CORRECTION November 11, 1975 Richard H. Hall; Daniel H. Haigh; Wesley L. Archer; Peter West It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Under "References Cited" insert:

[SEAL] 9/1966 Hoffenberg et al. 260/651 R X 2/1951 Erickson 260/651 R X 2/1951 West 260/651 R 8/1957 Heiberger et al. 260/651 R 9/1957 Heiberger 260/651 R 12/1960 Miller et al. 260/651 R Signed and Ersalcd this second Day Of March 1976 Arrest:

RUTH C. MASON Arresring Officer 

1. A CHLORINATED AROMATIC COMPOUND OF THE FORMULA
 2. The composition of claim 1 wherein the nitroalkane is nitromethane.
 3. The composition of claim 2 wherein the nitroalkane is present in a concentration of about 0.1-5 percent by weight.
 4. The composition of claim 2 wherein the chlorinated aromatic compound is benzyl chloride.
 5. The composition of claim 2 wherein the chlorinated aromatic compound is ( Alpha -chlorovinyl)toluene.
 6. The composition of claim 2 wherein the chlorinated aromatic compound is the crude reaction product obtained from the high temperature gas phase chlorination of vinyltoluene.
 7. The composition of claim 2 wherein the chlorinated aromatic compound is 1-chloromethylnaphthalene.
 8. The composition of claim 2 wherein the chlorinated aromatic compound is ethylbenzyl chloride.
 9. The composition of claim 2 wherein the chlorinated aromatic compound is Alpha , Alpha ''-dichloro-p-xylene
 10. The composition of claim 1 wherein the nitroalkane is nitroethane.
 11. The composition of claim 1 wherein the nitroalkane is a nitropropane. 